<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="container">
    <h2 class="page-header">Promise 封装 AJAX 操作</h2>
    <button class="btn btn-primary" id="btn">点击发送 AJAX</button>
    </div>
    <script>
        //接口地址 https://api.api.open.top/getJoke
        //获取元素对象;
        const btn = document.querySelector('#btn');
        btn.addEventListener('click',function(){
            //1.创建对象
            const xhr = new XMLHttpRequest();
            //2.初始化;
            xhr.open('GET','https://api.api.open.top/getJoke');
            //3.发送;
            xhr.send();
            //4.处理响应结果;
            xhr.onreadystatechange = function(){
                if(xhr.readyState == 4){
                    //判断响应状态码 2xx;
                    if(xhr.status >= 200 && xhr.status < 300){
                        //控制台输出响应体;
                        console.log(xhr.response);
                    }else{
                        //控制台输出响应状态码;
                        console.log(xhr.status);
                    }
                }
            }
        }) 
    </script>
</body>
</html>